106 



PSYCHE. 



[July iSqi. 



A NEW SIMULIUM FROM SOUTHERN NEW MEXICO. 



BY C. H. TYLER TOWNSEND, LAS CRUCES, N. M. 



In the southern part of New Mexico, 

 along the valley of the Rio Grande, 

 there begins to appear about the first of 

 May a buffalo gnat which is quite as 

 troublesome, especially to man, as its 

 more eastern congener, S. pectiarum. 

 It proves to be an undescribed species. 

 The first individuals that I have noticed 

 this year were in an orchard near Me- 

 silla on the 7th of May, and they were 

 at that date swarming in considerable 

 numbers. Mesilla is about a mile from 

 the Rio Grande, which flows to the 

 west of the town. Gnats were found 

 also on same date but in less numbers 

 on the college grounds, which are situ- 

 ated about four miles from the river. 

 The river rises in May, overflows all 

 the low areas lying adjacent to it, and 

 becomes a roaring, rushing body of 

 water. Its volume is dependent on the 

 amount of snow in the foot-hills to the 

 north particularly in Colorado, and on 

 rains, which are only exceptionally a fac- 

 tor. The snow in the canons exerts little 

 influence, for its thaw is so gradual as not 

 to be felt. I give these data for what 

 bearing they may have on the breeding 

 habits of this species. It is well known 

 that Simulium breeds in running water, 

 and our species no doubt is dependent 

 on the rise of the Rio Grande for its 

 appearance. Doubtless, also, it is dis- 

 tributed through the valley by the 



system of acequias or irrigation ditches 

 in use in this country, which open 

 from the river on a higher level to the 

 north, and furnish the only source of 

 water supply for the raising of crops. 

 This is an adverse bearing of the ques- 

 tion of riparian irrigation on injurious 

 insects. The securing of artesian water 

 and shutting off of the river water would 

 no doubt lessen the dispersion of the 

 gnats through the valley. 



From the first part of May the gnats 

 increase in numbers, until by the middle 

 or last of that month the}' are very 

 abundant in all parts of the valley. It 

 is usually between this time and the 

 middle of June that the river is at its 

 highest point. The)* are then to be 

 found on the mesa to the east toward 

 the Organ Mts., and may be met with 

 also on the elevated mesa nearer the 

 mountains, especially to the north. On 

 May 17th I observed them on the sum- 

 mit of the first mountain at the eastern 

 end of the Dofia Ana range, which is 

 nearer the river than the Organs, and 

 farther north. The elevation is at least 

 4,500 (probably 5,000) ft. above sea 

 level, or about 1,500 (perhaps 2,000) 

 ft. above the level of the river. They 

 are not found in the Organ Mts., which 

 are about twenty miles east of the river, 

 nor on the plains to the east and south 

 of them, though on the mesa to the 



